Mercedes-Benz F700 Concept

Mercedes reinvents the wheel. Well, the engine, at least, with a DiesOtto in this concept.

As car buyers bemoan rising fuel prices, manufacturers are responding with ever more fuel-efficient vehicles. At the Frankfurt auto show, everything from the Ford ECOnetic Focus to the VW Golf BlueMotion will try to woo environmentally conscious buyers with technology designed to get more miles out of every gallon.

The same is true for Mercedes-Benz, which will use the show to unveil its DiesOtto powertrain in the F700 concept sedan ("F" denotes a research vehicle). The engine defies conventional gearhead wisdom, producing 238 horsepower and 295 pound-feet of torque while still managing an estimated 39 mpg—all from a 1.8-liter engine that runs on conventional gasoline—no synthetic fuels.

These impressive figures are a result of a host of new engine technologies. The basic engine is a turbocharged 1.8-liter four-cylinder with direct-injection technology. Mercedes says that experimental technology gives the car the economy and torque of a diesel engine while maintaining the performance of a gasoline engine.

The DiesOtto has a variable compression ratio (to optimize performance under different engine loads and speeds) and compression ignition (where combustion occurs without spark plugs). It might eventually feature a hybrid drive to further increase fuel savings.

Although they may sound far-fetched, these technologies aren't without precedent. Saab has experimented with variable-compression engines, and GM recently demonstrated gasoline engines employing compression ignition.

The end result is a small, fuel-efficient engine with enough grunt to power a large car, in this case the five-door F700, which is a research vehicle similar in size to the Mercedes S-class luxury sedan.

The engine technologies demonstrated in this concept could make their way into future production Mercedes powertrains, as the automaker says it sees the DiesOtto technology package as a blueprint for the future of a gasoline engine with the fuel economy of a diesel.